Method for regenerating adsorbent by heating

ABSTRACT

A heat-regeneration method of an adsorbent containing an adsorbed substance wherein the heat-regeneration can be conveniently and efficiently carried out. It provides a method for regenerating an adsorbent by desorbing an adsorbed substance which has been adsorbed to the adsorbent through heating, wherein said method is a heat-regeneration method of the adsorbent which comprises irradiating a microwave or applying a high-frequency wave to the adsorbent containing the adsorbed substance in the presence of a magnetic material having a Curie point of from 50 to 350° C. to thereby allow the magnetic material to generate heat and to simultaneously heat the adsorbent by the generated heat.

TECHNICAL FIELD

The present invention relates to a heat-regeneration method of a spentadsorbent containing an adsorbed substance, and to an adsorbent.

BACKGROUND ART

As adsorbents, particulate or fibrous activated carbon, silica gel,alumina, zeolite and the like are known. These adsorbents are used foradsorption of adsorptive substances such as organic compounds. However,after the adsorption treatment, it is necessary to regenerate theadsorbents by heating them to release the adsorbed substances.

As a heat-regeneration method of an adsorbent containing an adsorbedsubstance, a method of bringing the adsorbent into contact with steam offrom 105 to 150° C. is generally adopted. In this method, since thedesorbed substance from the adsorbent is a mixture with the steam, amethod of liquefying the mixture with cooling and separating thedesorbed substance from water formed through condensation of the steamis carried out in order to recover the desorbed substance.

However, such desorption and regeneration using steam generally requirehuge facilities and steam management. In addition, since the heating ofthe adsorbent by steam is carried out by external heat transmission, theheat efficiency is not so high. Furthermore, when heat loss over thewhole facilities is considered, the heat efficiency is considerably low.Accordingly, the running cost is high at present. Moreover, since thedesorbed substance should be separated from water, the recovery of thedesorbed substance requires strict water management for preventingenvironmental pollution.

A method for heat-desorption of an adsorbed substance from an adsorbentusing no steam but microwave irradiation has been also proposed but thismethod involves problems that temperature control and homogeneousheating of the adsorbent are difficult, so that the method has not beensatisfactory yet.

An object of the present invention is to provide a heat-regenerationmethod of an adsorbent containing an adsorbent wherein theheat-regeneration can be conveniently and efficiently carried out, andan adsorbent.

DISCLOSURE OF THE INVENTION

The present inventors have investigated earnestly in order to solve theabove problems and completed the present invention.

That is, the present invention provides a method for regenerating anadsorbent by desorbing an adsorbed substance which has been adsorbed tothe adsorbent through heating, wherein said method is a heatregeneration method of the adsorbent which comprises irradiating amicrowave or applying a high-frequency wave to the adsorbent containingthe adsorbed substance in the presence of a magnetic material having aCurie point of from 50 to 350° C. to thereby allow the magnetic materialto generate heat and to simultaneously heat the adsorbent by thegenerated heat.

Also, the present invention provides an adsorbent comprising anadsorbent and a magnetic material, wherein the magnetic material has aCurie point of from 50 to 350° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a change of the temperature of a magnetic material withtime when a microwave is irradiated to the magnetic material.

FIG. 2 shows a relationship between the temperature of a magneticmaterial and the irradiating power when a microwave is irradiated to themagnetic material.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention relates to a method for regenerating an adsorbentin which the adsorbent containing an adsorbed substance is heated tothereby release the adsorbed substance from the adsorbent, wherein saidmethod comprises irradiating a microwave or applying a high-frequencywave to the adsorbent containing the adsorbed substance in the presenceof a magnetic material to thereby allow the magnetic material togenerate heat and to heat the adsorbent by the generated heat.

As a result of extensive studies on the method for regenerating anadsorbent containing an adsorbed substance by heating the adsorbent, thepresent inventors have found that the adsorbent can be conveniently andefficiently regenerated when the adsorbent is irradiated with amicrowave or applied with a high-frequency wave (hereinafter alsoreferred to as “irradiated with a microwave or the like”) in thepresence of a magnetic material to thereby allow the magnetic materialto generate heat and the adsorbent is heated by utilizing the generatedheat.

FIG. 1 shows a change of the temperature of a magnetic material having aCurie point of 140° C. when a microwave of 200 W is irradiated to themagnetic material.

As is apparent from FIG. 1, the temperature of the magnetic material israpidly raised by the microwave irradiation and is kept at a constanttemperature (close to the Curie point).

In the heat generation of the magnetic material by microwaveirradiation, when the microwave power (W) is variously changed as shownin FIG. 2, the present inventors have confirmed that the temperature ofthe magnetic material does not vary greatly by irradiation with amicrowave of from 100 to 300 W and is not increased to a temperatureequal to or higher than the Curie point.

The reason why the temperature of the magnetic material is not increasedto a temperature equal to or higher than the Curie point is that themagnetic material loses its magnetism at a temperature equal to orhigher than the Curie point and hence heat generation does not occur.

The heat-generation behavior of the magnetic material by the microwaveirradiation as shown above exhibits that it is very suitable as aheating method of an adsorbent containing an adsorbed substance.

Namely, the fact that the temperature of the magnetic material is notraised to a temperature equal to or higher than the Curie point meansthat a heating operation can be safely carried out.

Moreover, the fact that the temperature-increasing rate of the magneticmaterial at the microwave irradiation is large means that the heating ofthe adsorbent takes only a short time and hence the adsorbent can beefficiently heated.

By the microwave irradiation of the magnetic material, the magneticmaterial can be allowed to generate heat usually at atemperature-increasing rate of from 20 to 200° C./minute.

According to the present invention, when the magnetic material ishomogeneously dispersed in an adsorbent or an adsorbent-packed bed andis irradiated with a microwave or the like in this state to generateheat, the adsorbent-packed bed can be homogeneously and rapidly heatedevenly with good energy efficiency to a predetermined temperature (Curiepoint).

In the case where the magnetic material is irradiated with a microwaveor the like to generate heat, as mentioned above, the temperatureachieved by the heat generation becomes a constant temperature (close tothe Curie point) without particularly depending on the intensity of themicrowave or the like. Therefore, in the case where an adsorbent oradsorbent-packed bed in which the magnetic material is dispersed isirradiated with a microwave or the like for heating, since the adsorbentor the bed reaches a constant temperature (close to the Curie point),the whole adsorbent-packed bed can be homogeneously heated to apredetermined temperature (close to the Curie point) even when it isirradiated with a microwave or the like in one direction.

As the adsorbent used in the present invention, various adsorbentshitherto known can be employed. Examples of the adsorbents includeactivated carbon, silica gel, alumina, magnesia, calcia, silica-alumina,zeolite, and the like. The shape of the adsorbent may be any of variousshapes such as powdery, fibrous and granular shapes, and is notparticularly limited.

As the magnetic material used in the present invention, those having aCurie point of from 50 to 350° C., preferably from 100 to 200° C., canbe employed. Examples of the magnetic materials include soft magneticferrite (Curie point of from 100 to 350° C.) such as nickel-zincferrite, garnet-based ferrite (Curie point of from 100 to 300° C.) suchas yttrium-iron garnet, an alloy (Curie point of from 50 to 350° C.)such as iron-chromium, an elemental metal (Curie point of 300° C. orhigher) such as nickel, and the like.

In the present invention, an adsorbent is irradiated with a microwave orthe like in the presence of the magnetic material. In this case, theadsorbent is usually used in the form of a packed bed which is packed ina container, a column or the like. For homogeneous heating of the packedbed, it is preferable to disperse the magnetic material homogeneously inthe packed bed.

As a method for obtaining a packed bed in which the magnetic material ishomogeneously dispersed, there is a method of homogeneously mixing anddispersing the magnetic material in the adsorbent at the time when theadsorbent is packed in a container or a column and then packing themixture. In the case of mixing the adsorbent with the magnetic material,the shape of the magnetic material may be a shape capable of easy mixingwith the adsorbent and, according to the shape of the adsorbent, themagnetic material can be used in a powdery, granular or the like shape.Moreover, a method of using a molded product composed of a mixture of anadsorbent and a magnetic material and a method of using a productwherein a magnetic material is contained in or supported on an adsorbentare also preferable.

In the case where an adsorbent and a magnetic material are mixed andpacked into a packed tower, the ratio of the magnetic material is from0.05 to 50% by volume, preferably 0.1 to 20% by volume, and morepreferably from 0.5 to 10% by volume, based on the total amount of theadsorbent (in the state containing no adsorbed substance) and themagnetic material.

The preferable adsorbent used in the present invention is an adsorbentwherein a magnetic material is supported on or contained in an adsorbentbeforehand. Such an adsorbent is a molded product obtainable by moldinga mixture of a powdery adsorbent and a powdery magnetic material into arequired shape. In this case, a binder is used as a molding auxiliary.The binder may be any of conventionally used binders and, for example,water, bentonite, water glass, a polymeric substance, or the like can beused.

In addition, an adsorbent prepared by a method of partially or whollyimparting magnetism in a step of synthesizing the adsorbent, anadsorbent wherein a magnetic material in an ultra-fine particle form issupported on or adhered to the adsorbent, an adsorbent which is adheredto the surface of the magnetic material, and the like are alsopreferable.

The shape of the molded product may be any of various shapes such asspherical, columnar, and cylindrical shapes.

Since such a molded product and an adsorbent on which a magneticmaterial is supported contain a magnetic material therein, heatgeneration occurs when they are irradiated with a microwave or the like.In the present invention, the ratio of the magnetic material in themolded product or adsorbent is suitably set at from 0.05 to 50% byvolume, preferably from 0.1 to 20% by volume, and more preferably from0.5 to 10% by volume.

In the microwave used in the present invention, its wavelength is from10 MHz to 25 GHz, and is preferably an ISM frequency band. In general, amicrowave of about 2.45 GHz is employed. Moreover, in the high-frequencywave used in the present invention, its wavelength is from 1 KHz to 10MHz, and preferably from 10 KHz to 1 MHz.

For preferably carrying out the present invention, first, in theadsorption step, a gas containing an adsorptive substance is suppliedthrough the adsorbent or packed bed in which the magnetic material isdispersed and thereby the adsorptive substance is adsorbed to theadsorbent.

Then, in the desorption step, the packed bed is irradiated with amicrowave or the like. The magnetic material present in the packed bedabsorbs the microwave or the like to generate heat, and the adsorbent isheated by the generated heat. Thereby, the adsorbed substance containedin the adsorbent is desorbed and recovered. In the case where theadsorptive substance is an organic solvent, the gaseous organic solventdesorbed from the adsorbent in the desorption step is liquefied withcooling and is recovered.

The adsorptive substances to be adsorbed to the adsorbent includevolatile organic compounds (e.g., aromatic solvents such as benzene,toluene and xylene, alcohols, organic amines, ketones, aldehydes, etc.),and polar gases (e.g., sulfurous acid gas, carbon dioxide gas,nitrogen-containing gases, etc.).

EXAMPLES

The present invention is described below in more detail with referenceto Example.

Example 1

A mixture of hydrophobic zeolite as an adsorbent and nickel-zinc ferrite(Curie point of 140° C.) (content of nickel-zinc ferrite: 20% by volume)was press-molded into particles having a diameter of about 1 mm and 1 gof the particles was packed in a glass tube having a diameter of 8 mm toprepare an adsorption column.

Then, helium containing 500 ppm of benzene as an adsorptive substancewas supplied through the adsorption column at a temperature of 25° C. toadsorb the benzene to the adsorption column.

Next, a microwave (300 W, wavelength: 2.45 GHz) is irradiated to theadsorption column under circulation of helium. As a result, thetemperature of the adsorption column was rapidly raised(temperature-increasing rate: about 150° C./minute) and the temperaturereached around 140° C., which is the Curie point of nickel-zinc ferrite,within 1 minute of the microwave irradiation, the temperature beingstabilized at this temperature.

The benzene concentration in the helium flown through the adsorptioncolumn rose at a stretch immediately after the microwave irradiation andthe whole amount of the benzene adsorbed to the adsorbent was desorbedwithin 5 minutes after the start of the microwave irradiation. Thehelium containing the desorbed benzene was cooled and thereby thebenzene contained in the helium was liquefied and recovered.

INDUSTRIAL APPLICABILITY

In accordance with the heat-regeneration method of an adsorbentaccording to the present invention, an adsorbed substance can bedesorbed with a high heat efficiency since it is not necessary to usesteam. In addition, the method requires only a compact apparatus andhence the running cost is remarkably reduced.

1. A method for regenerating an adsorbent by desorbing an adsorbedsubstance which has been adsorbed to the adsorbent through heating,wherein said method is a heat-regeneration method of the adsorbent whichcomprises irradiating a microwave or applying a high-frequency wave tothe adsorbent containing the adsorbed substance in the presence of amagnetic material having a Curie point of from 50 to 350° C. to therebyallow the magnetic material to generate heat and to simultaneously heatthe adsorbent by the generated heat.
 2. The method according to claim 1,wherein the adsorbent contains the magnetic material in a dispersedstate.
 3. The method according to claim 1, wherein the adsorbentcontaining no magnetic material is kept in the form of a packed bed andthe magnetic material is dispersed in the packed bed.
 4. An adsorbentcomprising an adsorbent and a magnetic material, wherein the magneticmaterial has a Curie point of from 50 to 350° C.